The heat that we feel from our Sun or from a fireplace is infrared radiation (thermal energy). Even objects that we think of as being very cold, such as ice cubes, emit thermal energy. Measuring the infrared energy from astronomical objects is difficult because most of it is blocked by Earth’s atmosphere. Therefore, most infrared astronomers use space telescopes to study the thermal emission from celestial objects.
Infrared Astronomy is the detection and study of the infrared radiation (heat energy) emitted from objects in the Universe. Every object that has a temperature radiates in the infrared. So, Infrared Astronomy involves the study of just about everything in the Universe. In the field of astronomy, the infrared region lies within the range of sensitivity of infrared detectors, which is between wavelengths of about 1 and 300 microns (a micron is one millionth of a meter). The human eye detects only 1% of light at 0.69 microns, and 0.01% at 0.75 microns, and so effectively cannot see wavelengths longer than about 0.75 microns unless the light source is extremely bright.
The Universe sends us a tremendous amount of information in the form of electromagnetic radiation (or light). Much of this information is in the infrared, which we cannot see with our eyes or with visible light telescopes. Only a small amount of this infrared information reaches the Earth’s surface, yet by studying this small range of infrared wavelengths, astronomers have uncovered a wealth of new information.
In space, there are many regions which are hidden from optical telescopes because they are embedded in dense regions of gas and dust. However, infrared radiation, having wavelengths which are much longer than visible light, can pass through dusty regions of space without being scattered. This means that we can study objects hidden by gas and dust in the infrared, which we cannot see in visible light, such as the center of our galaxy and regions of newly forming stars.
SOFIA has the unique ability to fly above most of the infrared absorbing water vapor in our atmosphere and thereby allows for superior imaging quality and observational sensitivities in the IR region.
Credit: the above information taken from
https://www.nasa.gov/mission_pages/SOFIA/infrared_new_rd.html#.VddeD7XK-5J
countdownwithmrk 
“How much water vapor does SOFIA absorb?”
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Katie, SOFIA doesn’t absorb water vapor, it is an airplane that flies high enough to get above the water vapor that is in the atmosphere. It is that water vapor that absorbs infrared radiation, which makes infrared astronomy virtually impossible to do “on the ground”.
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“What kind of telescope measures infrared light?”
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Good Question Katie. Almost any type of telescope can be used, but to really “see” infrared light, you need special instruments hooked up to the telescope that are sensitive to those wavelengths of the electromagnetic spectrum.
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